1. Field of the Invention
The present invention pertains to apparatus for mixing liquid and pulverulent materials, and especially to mixing apparatus having a clamp plate for securing a container.
2. Description of the Related Art
An increasing variety of products offered for sale today are made available in slightly different compositions, requiring mixing at the point of sale to complete preparation of the product. For example, paint and paint products are mixed at the point of sale to provide a particular color chosen by the customer. This typically involves mixing a small quantity of tints or colorants in a much larger quantity of a relatively colorless base material. Thorough mixing of the colorants and base material is required to assume uniform color characteristics throughout the resulting paint product.
A variety of vibratory mixers have been proposed for use either at a manufacturing site or at points of sale. One particularly successful vibratory mixer is disclosed in U.S. Pat. No. 4,834,548 which vibrates a container clamped in the apparatus in a generally conical motion. The mixing motion has been found to be quite successful in producing uniform paint compositions. However, improvements have been desired in miniaturizing the apparatus and improving the clamping arrangement employed.
U.S. Pat. No. 4,134,689 discloses mixing apparatus having a different, vibratory motion with an inner frame driven from below by horizontally oriented cam members. A clamping plate is provided for the inner frame, by a pair of twin lead screws driven from above by a transmission shaft. The clamping plate travels up and down along the lead screws, as the lead screws are rotated. The twin lead screw design is costly to manufacture and adds to the weight of the mixing apparatus. Improvements in weight decrease for small, countertop units have prompted investigations for other mixer designs.
U.S. Pat. No. 4,789,245 discloses a disc-type mixing apparatus having a crank-operated clamping plate. The clamping plate and associated mechanism are attached to a rotating disc, leading to a relatively large, bulky package unsuitable for some applications such as a countertop mixing unit. British Pat. No. 1 310 655 discloses a mixing apparatus having a clamping plate moved up and down by an operating rod attached to the plate. The rod passes through a frame member to which a quick-locking device is mounted. The locking device is actuated by a horizontal shaft which is rotated about the rod between unclamped and clamped positions. The clamping plate is supported at the center by a single rod to which a clamping force is applied to maintain the pressure plate in a fixed position. It is desired to provide a quick-acting pressure plate clamped at least two spaced apart points.